An electronic Integrated Circuit (IC) is a device having integration of electronic circuits and components onto the surface of a substrate of a semiconductor material by processes of fabrication. The substrate materials include, but are not limited to, silicon (Si), Silicon on insulator (SOI), germanium (Ge), indium phosphide (InP), gallium arsenide (GaAs), gallium nitride (GaN) etc. Majority of the electronic integrated circuits; however, are fabricated on silicon due to their low cost of fabrication and the high reliability of silicon electronics. GaAs, InP, and GaN are used only occasionally. For example, GaAs and InP are used when high speed is required and GaN is used when high power is required. In electronics, an integrated circuit can also be referred to as a microcircuit, a microchip, a silicon chip, or simply a chip. Integrated circuits include a combination of active electronic devices with passive components onto a single semiconductor crystal. The examples of active electronic devices include, but are not limited to, transistors, diodes etc. The examples of passive components include, but are not limited to, resistors, capacitors, inductor etc. The processes involved in the fabrication of integrated circuits can include, but are not limited to, vapor-phase deposition of semiconductors and insulators, oxidation, solid-state diffusion, ion implantation, vacuum deposition and sputtering etc.
Electronic Integrated Circuits (ICs) have demonstrated a combination of low cost, high reliability, low power requirements, and high processing speeds compared to the previously existing techniques of vacuum tubes and discrete transistors. Applications of Integrated circuits include, but are not limited to, computing, communications, manufacturing and transport systems, the Internet, computers, cellular phones, and other digital appliances.
A Photonic Integrated Circuit (PIC) is a device that integrates multiple photonic functions. The difference between the PIC and an IC is that the PIC process signals are imposed on optical beams while IC process signals are imposed on electrical currents or voltages. These optical beams typically have wavelengths ranging from the UV/visible spectrum (200-750 nm) to near Infrared spectrum (750 nm-1650 nm). The Photonic Integrated Circuit can also be interchangeably referred to as an Integrated Optical Circuit. The materials used for the fabrication of PICs include, but are not limited to, silica (SiO2) on silicon, silicon on insulator (SOI), various polymers and compound semiconductor materials such as GaAs, InP, and GaN. Integrated photonic devices can also be classified into “passive photonic devices” that do not consume or exchange energy; “emissive/absorptive photonic devices” that involve light emission, optical gain, and absorption, or electronic energy level transitions that give rise to the spontaneous emission, stimulated emission, or absorption of photons; “electro-optic devices” that require an applied electrical voltage or current but do not require optical emission/absorption for their main functionalities; and nonlinear optical devices that involve nonlinear-optical properties of materials. Passive devices include, but are not limited to, optical beam splitters, optical wavelength filters, optical resonators, optical waveguides, optical wavelength multiplexers, optical couplers, optical polarizers, optical isolators, polarization rotators etc. Emissive devices include, but are not limited to, optical amplifiers, lasers, and light-emitting devices. Absorptive devices include photodetectors etc. Electro-optic devices include, but are not limited to, electro-optic modulators, electro-optic phase shifters, electro-optic switches, etc. Nonlinear-optical devices include second harmonic generators, photonic transistor, and all-optical switches etc. Emissive/absorptive, electro-optic, and nonlinear optical devices together are part of “active devices” that are devices that consume or exchange energy. Beside the above, there are other active devices such as opto-mechanical devices that involve mechanical power but the above are the main classes of active photonic devices of interest here. These active devices of interest are sometimes classified into optoelectronic devices (those that involve applied electrical power) and all optical devices that do not involve applied electrical power. All optical devices are typically devices that involve direct interaction of light with light. These nomenclatures are not always precise in usage and are defined above specifically for their application here.
The fabrication techniques for PIC are typically similar to the fabrication techniques used in ICs. In the fabrication process, the PIC devices that can be mounted on a PIC chip include, but are not limited to, the above mentioned passive, active, and electro-optic devices, with applications ranging from the field of fiber-optic communication, computing, sensing, to biomedical.
Typically photonic integrations are of two types; namely, Hybrid and Monolithic integrations. Monolithic integration involves “wafer-level” processes that result in many devices on a single substrate. Hybrid integration involves fabrication of individual devices separately before placing them together to form a subsystem in a packaged module. Monolithic integration can take advantage of the economy of scale much better than hybrid integration, as the production cost per wafer in monolithic integration does not vary too much with wafer size. However, larger wafer size provides integration of many devices on the wafer, resulting in much lower cost of manufacturing per device. The production of monolithic photonic integrated circuits involves construction of the PIC devices on a common substrate using wafer-level processes.
The most common function of the PIC device is to optically transmit data. Optical Data Transmission requires various steps such as sending light by using lasers, splitting the light into different wavelengths by using wavelength multiplexers or optical filters or optical resonators, encoding data by using modulators or direct current modulation of semiconductor lasers, and receiving data by using photo detectors, as are known to those skilled in the art. Further, the optical data transmission also requires low loss interconnect waveguides. As is known to those skilled in the art, the Optical Data Transmission using photonic circuit typically is capable of substantially higher data transfer rates than Electrical Data Transmission using electronic circuit, and at the same time eliminates problems resulting from electromagnetic interference. PICs can allow optical systems to be more compact and perform higher functionally as compared to discrete optical components.
A main challenge in photonic device integration is that photonic devices are typically large in size as compared to the electronic devices. They have typical sizes of hundreds of micrometers to millimeters or centimeters. As known to those skilled in the art, to address the challenge, photonic devices that are much smaller in size have been realized recently by utilizing photonic device waveguide structures that have high refractive index contrast between the waveguide core and waveguide cladding. These photonic devices are referred to as dielectric ‘nanophotonic devices’. As is known to those skilled in the art, dielectric nanophotonic devices include, but are not limited to, photonic bandgap devices, photonic crystal devices, microring resonators, microdisk resonators, super-prisms, photonic crystal based slow or fast wave devices, photonic-wire waveguides, and nano-lasers. There are also small photonic devices realized with photonic device structures that involve electron plasma in metals, which are referred to as plasmonic nanophotonic devices. The dielectric and plasmonic nanophotonic devices below will be referred to as nanophotonic devices. As is known to those skilled in the art, plasmonic nanophotonic devices include, but are not limited to, plasmonic waveguides, plasmonic lasers, plasmonic ring and disk resonators, plasmonic photonic crystals, surface plasmon devices, plasmonic slow-wave devices, plasmonic fast-wave devices, and negative dielectric or negative refractive index devices. The optoelectronic or all-optical versions of such devices will be referred to as nano-optoelectronic devices and nano all-optical devices, respectively. Nanophotonic devices have typical device sizes of nanometers to hundreds of micrometers at the optical wavelength of about one micrometer and are substantially smaller than conventional photonic devices. As is known to those skilled in the art, the physical size of the device scales somewhat proportionally to the electromagnetic wavelength of operation. Hence, the physical size examples given here are not absolute but shall scale somewhat proportionally to the electromagnetic wavelength of operation.
Photonic integrated circuits and electronic integrated circuits complement each other in fulfilling the demanding performance requirements of high-speed communications and high-performance computing etc. However, at present photonics and electronics are still handled by different materials platforms and technologies. While ultra-large-scale integration of electronics has become a reality, the large-scale monolithic integration of high-performance photonic circuits on a chip is still largely unaccomplished. It is expected that if photonic devices and electronic devices can be integrated in large scale on a same chip, new functionalities can be brought that will combine the high data transport rate of photonics with the high data processing speed of electronics, resulting in an integrated Electronic-Photonic Integrated Circuit (EPIC) that will be much faster than IC or PIC alone.
In light of the foregoing, there exists a need for a technology that could realize integration of photonic devices on a chip in a way that is compatible with electronic device integration.
At present, majority of the large-scale electronic integrated circuits are fabricated with silicon material and majority of the active photonic or nanophotonic devices are fabricated with compound semiconductor materials such as InP, GaAs, or GaN. The fabrication process of electronic devices for silicon electronics such as those used in fabricating CMOS (Complementary Metal Oxide Semiconductor) transistors involve temperatures around 1000° C. Most compound semiconductors cannot withstand such high temperatures without suffering from chemical decomposition. A method that will address such incompatibility and enable the fabrication of photonic or nanophotonic devices in a way that will be compatible with electronic devices will be of interest.
Furthermore, current photonic integrated circuit technology is not favorable due to various issues, including the difficulty in achieving low-loss and cost-effective coupling of light from optical fiber into the photonic chip, the cost of integration of compatible optoelectronic and all-optical devices on the chip, the integration of optoelectronic devices on the chip, the integration of the newer generation of nanophotonic and nano-optoelectronic devices on the chip, and the integration of passive photonic devices on the chip.
In light of the foregoing, there exists a need for a technology that could achieve large scale integration of photonic devices on a chip with efficient and cost-effective optical coupling to optical fiber, and that could achieve low fabrication cost in the integration of compatible optoelectronic and all optical devices on the chip, the integration of optoelectronic devices on the chip, the integration of the newer generation of nanophotonic and nano-optoelectronic devices on the chip, and the integration of passive photonic devices on the chip, and preferably do so in a way that is compatible with electronic device integration.